I like to bike when I can, but I’m still nervous to leave it even with a U-lock around the frame. I’ve also had a seat stolen before (not even a good one), but I’m not sure if there’s anything reasonable to do about that.
What do you do to lock up your bike for commuting?

My primary defense is the lock it inside limited access bike rooms - I have my own spot in a bike shed that only people paying for a bike parking spot can access at my home, and at work there’s a bike room that requires a badge to access.
Additionally, I have a folding lock that I fold around some kind of secure piece of metal, through the frame and the back wheel.
When out and about, I try to leave the bike where I am able to see it, in daylight, in places where there’s a good amount of foot traffic.
These strategies have worked out so far. I’m considering upgrading to a U-lock, but I’ve so far been reluctant as I fear it may reduce the amount of places where I can lock the bike to.